Reproducible perovskite solar cells using a simple solvent-mediated sol−gel synthesized NiO _x hole transport layer

<jats:title>Abstract</jats:title>
<jats:p>A nickel oxide (NiO<jats:italic>
<jats:sub>x</jats:sub>
</jats:italic>) hole transport layer was made from nickel oxide powder by a simple process and non-stabilizer or chelating agent. We used ethanol as the main solvent and less than 2% nitric acid as the co-solvent. The formation reaction mechanism of the NiO<jats:italic>
<jats:sub>x</jats:sub>
</jats:italic> thin film was also studied. Perovskite solar cells (PSCs) with an optimum thickness of 70 nm exhibited a power conversion efficiency as high as 12.99%, which is superior to those of PSCs with their counterparts. The moisture stability of NiO<jats:italic>
<jats:sub>x</jats:sub>-</jats:italic>based devices (non-encapsulated) remained above 70% of their initial output after 700 h storage at ambient conditions.</jats:p>